A window motor or wiper motor may or may not have the power needed; plus there's the possibility of stripping gears. I would actually use linear actuators with built in feedback potentiometers (whether you'll want to use one or two is up to you). Such actuators are more robust, can be found in waterproof versions, and generally also have built-in end-stop switches. They are driven just like a DC motor; in theory, you could even apply the idea of the "servo-conversion" to one, as long as it has a feedback potentiometer (or you use an external one).
Just make sure you get the proper one - some have different ratings for pull vs. push (extend/retract), some use a pulse output for position sensing (so you count pulses to determine where it is positioned), some are designed so that they can be "back-driven" (you may or may not want that?) - and of course, you need to determine how fast the extension/retraction will need to occur.
They also aren't cheap, but then again, you are talking about making this a part of your vehicle - you -do not- want to skimp on something like this (especially when it comes to speed controls on wheels); or at least I would think you wouldn't want to...
Here's a dealer of such devices, but look around for others - there are many manufacturers (and several have ones designed for automotive purposes - but generally for things like opening hoods or trunks; apps of that nature):