Personally I'd prefer to see weapons that would more benefit The Thing's era, and time setting, so:
1) Instead of the Bwutal D0w0m flamethrower opt instead for a better sprite (i.e such as the
really bad example Flammenwerfer from uhh Moon Man.pk3 {this is the only source I could think of off the top of my head that uses that flamethrower, sorry])
2) Use the VietDoom M16 instead of the bd19 AR (not exactly accurate considering that VD's is a M16A1, and a M16A2 would be a better option, but gotta work with what you gotta work with) and give it a burst-function instead of semi-auto.
3) Eschew the Gauss Cannon entirely, maybe replace it with the Grenade Launcher, make it a M79, have it be reloadable, maybe even got the RE2-route and give it incendiary rounds or something.
4) Replace the 5 Slot GL with Dynamite (I can provide you with proper tan-colour Dynamite sprites based on the Thing mind you, as I'm using such a weapon for RN)
5) Maybe instead of using a greyscaled Shotgun, and just replace it with VD's Ithaca M37 (that appeared in The Thing according to IMFDB)
6) Replace the starting weapon with a .44 Revolver (something like what MacReady uses in the movie, just upscale it for .44 so it's not pointless, once again VD has the assets for it so
)
Just suggestions, not dictating
You mention making a mapset, you might wanna check out Cold as Hell, since that's basically The Thing From Another World meets Doom.