You didn't follow my screenshot, you also have to set spawnflags 1 to set it to solid - use the mins and maxs from my new screenshot, they match the rock more closely - the modelscale and modelscale_vec keys will also scale your mins and maxs so those should always be calculated from the default scale of the model. Of course you can also freely scale your model with the modelscale_vec key but then you might have to use offsets to the mins and maxs usually used. You can also set those to close a gap in your map perfectly if you don't scale the model with modelscale or modelscale_vec - otherwise you have to take those into consideration too and calculate your mins and maxs with this factor per axis.
You don't need mass, gravity, the damage stuff or the material - but the material helps when impactsparks are generated.
Here's the list of materials:
"material" - default is "0 - MAT_METAL" - choose from this list:
0 = MAT_METAL (basic blue-grey scorched-DEFAULT)
1 = MAT_GLASS
2 = MAT_ELECTRICAL (sparks only)
3 = MAT_ELEC_METAL (METAL2 chunks and sparks)
4 = MAT_DRK_STONE (brown stone chunks)
5 = MAT_LT_STONE (tan stone chunks)
6 = MAT_GLASS_METAL (glass and METAL2 chunks)
7 = MAT_METAL2 (electronic type of metal)
8 = MAT_NONE (no chunks)
9 = MAT_GREY_STONE (grey colored stone)
10 = MAT_METAL3 (METAL and METAL2 chunk combo)
11 = MAT_CRATE1 (yellow multi-colored crate chunks)
12 = MAT_GRATE1 (grate chunks--looks horrible right now)
13 = MAT_ROPE (for yavin_trial, no chunks, just wispy bits )
14 = MAT_CRATE2 (red multi-colored crate chunks)
15 = MAT_WHITE_METAL (white angular chunks for Stu, NS_hideout )
Well you can check out the saboteur NPC and assign a different model to it, see if the stealth still works on it - from there on out you could make any kind of NPC as long as the class is what makes it cloak...