If your going with rhinos then knowing the risks for them is gonna be a must. Countering those risks is very limited, to literrally a turn or two when your men are inside, but very much cheap and easy to do. Use of smoke launchers and extra armour will give the rhinos a better chance of surviving one turn at the very least, and playing on a 4 foot field with 6 inch depoyement means that you shouldn't have to much land to cross in the next turn anyway.
If your gonna mount the four then realise that those that survived after popping their smoke should proceed by walking the last of the distance while the rhinos speed ahead and form effective roadblocks or lines that hinder enemy line of sight. They die, they die, your opponent has wasted fire on them and done you the job of keeping models alive for another turn. If any survive then you got something to annoy your opponent with. therwise your troops should be in range to assault or just about to. Having escaped being shot at two times over one time.
BT's and cc are very predictable, but four rhinos worth of them is still hard to go up against and not be having a hard time when they can survive most of whats hitting them. Go for the four cc squads. 40 guys is always an evil amount of marines to be fielding...8)
Rhino: an effective transport amongst other things when you know what your doing with it.
Razorback: a good way for a devestator squad to get five heavy wepons.
Droppod: Ceramite herse, those who come out of it rarely live to tell the tale when they begin that close to their opponent and can only shoot. Also not always the best on helping when you need it when you do not have the favour of the dice gods.