I think I was blessed by the Random Number Gods for this run.
Shortly after clearing Hell's Arena, I stumbled upon a super shotgun and a red armour. I promptly discarded the double and continued on my merry way, collecting up to seven blue armours at one point. On the way to Deimos I started progress on a fireshield. Cleared the Anomaly with little trouble, and then I tried my luck again at Deimos Lab. Prior attempts have all ended badly. By this point I had two envirosuits in my inventory. There I found another super shotgun, and the resources to make two thirds of a fireshield, and after killing both shamblers, half of a fireproof armour. I also learned how to make a speedloader pistol. I also found a unique mod, but I don't think the firestorm mod helps shotguns much.
Next floor gave me the rest of the fireproof armour supplies, and I had attained Fireangel before spanking the cyberdemon. A few floors later, I assembled another fireproof armour because I could (when is this ever a valid justification). Along the way I also picked up a gothic armour and had a supply of pristine blue armours.
And then, Dis...
I had reached the Spider Mastermind a few times in 0.9.9.6, all of which ended with me reduced to a red smear. I have reached Dis twice now in 0.9.9.7.
0.9.9.7 HNTR Spider Mastermind is a pansy. 
With my shotguns, I was hoping to build a nano-shrapnel super shotgun and/or a plasmatic shrapnel super shotty. I never found any advanced mods other than the firestorm weapons pack. I also never found the Jackhammer :<.
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 DoomRL (0.9.9.7) roguelike post-mortem character dump
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 Pancor, level 10 Former Human Lance Corporal Technician,
 defeated the Mastermind at the City of Dis.
 He survived 100712 turns and scored 93431 points. 
 He played for 1 hour, 54 minutes and 37 seconds. 
 He didn't like it too rough.
 He killed 544 out of 544 hellspawn. (100%)
 This ass-kicking marine killed all of them!
 He was an Angel of Shotgunnery!
-- Special levels --------------------------------------------
  Levels generated : 11
  Levels visited   : 4
  Levels completed : 4
-- Awards ----------------------------------------------------
  Medal of Prejudice
  UAC Star (bronze cluster)
  Hell Armorer Badge
  Hell Champion Medal
  Veteran Bronze Badge
-- Graveyard -------------------------------------------------
  ###########################################################
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  ######........####.....####.....####........###############
  #####.........####.....####.....####.........##############
  ####..........####..............####..........#############
  ###............................................############
  ###....####............................####....############
  ###...&####............................####....############
  ###....####............................####....############
  ###....####............................####....############
  ###..........................%.................############
  ####..........####............X.####..........#############
  #####.........####.....####.....####.........##############
  ######........####.....####.....####........###############
  #######.......####.....####.....####.......################
  ########...............####...............#################
  #########................................##################
  ###########################################################
-- Statistics ------------------------------------------------
  Health 52/70   Experience 46704/10
  ToHit Ranged +0  ToHit Melee +0  ToDmg Ranged +0  ToDmg Melee +0
-- Traits ----------------------------------------------------
  Class : Technician
    Ironman          (Level 2)
    Hellrunner       (Level 2)
    Reloader         (Level 2)
    Dodgemaster      (Level 1)
    Whizkid          (Level 1)
    Shottyman        (Level 1)
    Fireangel        (Level 1)
  Rel->Rel->SM->HR->HR->WK->DM->MFa->Iro->Iro->
-- Equipment -------------------------------------------------
    [a] [ Armor      ]   blue armor [2/2] (114%) (B)
    [b] [ Weapon     ]   super shotgun (10d4)x2 [0/2] (P2)
    [c] [ Boots      ]   plasteel boots [2/2] (100%) (T)
    [d] [ Prepared   ]   shell box (x100)
-- Inventory -------------------------------------------------
    [a] super shotgun (9d4)x2 [2/2] (P1)
    [b] blue armor [2/2] (100%)
    [c] blue armor [2/2] (100%)
    [d] fireproof red armor [4/4] (100%)
    [e] red armor [4/4] (200%) (BT)
    [f] fireproof red armor [4/4] (100%)
    [g] gothic armor [6/6] (200%)
    [h] shotgun shell (x50)
    [i] shotgun shell (x50)
    [j] shotgun shell (x24)
    [k] shotgun shell (x50)
    [l] shotgun shell (x50)
    [m] shotgun shell (x50)
    [n] shotgun shell (x50)
    [o] large med-pack
    [p] large med-pack
    [q] large med-pack
    [r] large med-pack
    [s] large med-pack
    [t] shell box (x100)
-- Resistances -----------------------------------------------
    Acid       - internal 0%    torso 0%    feet 50%  
    Fire       - internal 0%    torso 0%    feet 25%  
    Plasma     - internal 0%    torso 20%   feet 0%   
-- Kills -----------------------------------------------------
    100 former humans
    67 former sergeants
    31 former captains
    88 imps
    56 demons
    125 lost souls
    14 cacodemons
    17 hell knights
    12 barons of hell
    7 arachnotrons
    3 former commandos
    5 pain elementals
    3 revenants
    2 mancubi
    8 arch-viles
    2 bruiser brothers
    2 shamblers
    1 Cyberdemon
    1 Spider Mastermind
-- History ---------------------------------------------------
  He started his journey on the surface of Phobos.
  On level 2 he entered Hell's Arena.
  He left the Arena as a champion!
  On level 7 he sneaked into the Phobos Lab.
  He broke through the lab.
  On level 8 he encountered the Phobos Anomaly.
  On level 9 he entered Deimos Lab.
  He destroyed the evil within and reaped the rewards!
  On level 10 he assembled a fireproof armor!
  On level 14 he ventured into the Halls of Carnage.
  On level 16 he found the Tower of Babel!
  On level 18 he assembled a fireproof armor!
  Then at last he found Dis!
  On level 24 he finally defeated the Mastermind.
-- Messages -------------------------------------------------- 
 You are hit! You are hit! You are hit! You are hit! You are hit! You are hit! 
 The Spider Mastermind hits you. 
 Fire -- Choose target... 
 You see : a Spider Mastermind (mortally wounded) | blood | [ m ]ore 
 Targeting canceled. 
 You use a large med-pack. You feel fully healed. 
 Fire -- Choose target... 
 You see : a Spider Mastermind (mortally wounded) | blood | [ m ]ore 
 The Spider Mastermind flinched! 
 The Spider Mastermind hits you. You dodge! You dodge! You dodge! You dodge! 
 You dodge! You are hit! 
 Fire -- Choose target... 
 You see : a Spider Mastermind (almost dead) | blood | [ m ]ore 
 The Spider Mastermind dies. Congratulations! You defeated the Spider 
 Mastermind! Press <Enter>... 
 You feel relatively safe now. 
-- General --------------------------------------------------- 
 9 brave souls have ventured into Phobos:
 7 of those were killed.
 2 souls destroyed the Mastermind...
 2 killed the bitch and survived.
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Two classes down, one to go. Maybe I'll deviate from AoSh... Or maybe post a mortem from less successful runs...