Modelling Assistance

I am in need for help.
I have created a model in blender of a vehicle to be used in blender. it has sub groups and whatnot too. The area inside a section of it is where players can walk around to build controls/buttons or what have you and put in chairs to drive, but when i test it out in Gmod, im always floating inside the model as if there is no space at all in it. Now I know it has something to do with the phys model, as I have created simple walls all around the area

https://orig00.deviantart.net/645e/f/2017/313/7/8/screen_by_zp92-dbt9kze.png

but no matter how many times I re compile after trying to fix what I think is wrong, nothing works. Not only that when I spawn it in gmod, almost half the model sinks into the ground. Looking atthe model in hlmv, it’s also on it’s side.

https://orig00.deviantart.net/59ec/f/2017/313/a/4/screen2_by_zp92-dbt9l6g.png

Here is the qc if that helps.

$modelname “zacks_trains/class08/Class08.mdl”

$bodygroup “Body”
{
studio “08_ref.smd”
}
$bodygroup “Hood”
{
studio “08_hood.smd”
}
$bodygroup “Buffers”
{
studio “08_buffers.smd”
}
$bodygroup “Back”
{
studio “08_back.smd”
}
$bodygroup “Cab”
{
studio “08_cab.smd”
}
$bodygroup “Bottom”
{
studio “08_bottom.smd”
}
$bodygroup “Grill”
{
studio “08_grill.smd”
}

$texturegroup “skinfamilies”
{
{ “yellow” }
{ “tan” }
{ “grey” }
{ “stripes” }

}

$staticprop

$surfaceprop “metal”

$contents “solid”

$maxeyedeflection 90

$cdmaterials “models\Class08”

$sequence “idle”{
“anims\08idle.smd”
fadein 0.2
fadeout 0.2
fps 30
}

$cbox 0 0 0 0 0 0

$bbox -64 -348 -40 64 320 140

$collisionmodel “08_phys.smd”
{
$mass 40000
$inertia 1
$damping 0
$rotdamping 0
$rootbone " "
$concave

}

Any advise you can offer would be greatly appreciated!