your lack of mobility is going to hurt you, but you could try to put together a large space marine gunline, though not too sure how effective it will be. Could do something like....
(
HQ) Captain w/ terminator armor
(T) Tactical Squad (10) w/ plasma gun, plasma cannon
(T) Tactical Squad (10) w/ plasma gun, plasma cannon
(T) Tactical Squad (10) w/ plasma gun, lascannon
(T) Tactical Squad (10) w/ plasma gun, lascannon
(E) Sternguard (6) w/ (6) combi-melta, razorback w/ assault cannon
(E) Mortis Contemptor Dread w/ (2) kheres assault cannon
(E) Terminator Squad (5) w/ whatever you want to outfit them with
(
HS) Centurion Devastator Squad (3) w/ grav cannons and hurricane bolters
(
HS) Thunderfire Cannon
This is somewhere around the 1800-1900 area. I don't have my book with me so I'm just guessing at rough point estimates. I would combat squad all the
tac squads and form a gunline. anchor that with the dreadnought, centurions, and thunderfire cannon. Send the sternguard up in the razorback and
DS the termies in with the captain. Honestly, there isn't much you can do in the way of a really competative list with this. You lack mobility. If you pick up some drop pods, you can drop 2 stern guard squads in at the very least to take out enemy armor or
MC's. Maybe convert the Captain to a Libby and stick him with the cents for added mobility/protection. Could also keep just one sternguard squad and instead roll with 2 dreads and spit out 24
str 6 rending shots per turn between the two of them

If you do go with this static gunline, invest in some sort of fortification to help them survive longer
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