truck gps

It takes some work, but use a GPS that allows you to create routes and combine that with a good trucker's atlas like from Rand-McNally. The atlas will show roads that can be used by large vehicles so you can plan your route accordingly.

Pretty much what the other responder said--class A motorcoaches are pretty much similar to Greyhound buses in size, so generally what you'll be looking for are POIs designed for the needs of truckers and other large commercial vehicles.

There are some specialised RV and trucker GPS programs out there, but (as you've found) these tend to be geared towards Windows or Windows Mobile users and are geared far more towards truckers and their specialised needs (such as rest havens for DOT-mandated rest breaks, etc.); more useful would be creating a POI set (or more properly, multiple POI sets) of low overpasses, RV-friendly parking, and so on. (I've seen a few commercial attempts at these, but these tend to be restricted to a specific chain. It'd be much better to get these in two or three consolidated POI lists.)

As previously mentioned, Rand-McNally actually has a pretty good specialised map (or more properly, series of mapbooks) designed specifically for commercial drivers that are usually available at truck stops (which, of note, there IS a POI here already of truck stops, and truck stops are almost invariably motorcoach friendly) that could be useful for a start; other trucker's atlases could also be used as a basis for setting up at least an "RVer's height warning/dimension warning" POI list. A safe bet for knowing which roads are going to be RV-friendly are roads that are "STAA roads" (designed for tall and long trucks), and low overpasses do tend to be flagged in these.

(This actually may be an interesting POI project to work on, to be honest.)

Another POI list I'm rather surprised hasn't been done yet (and which probably needs to be) is a POI list of national campgrounds that are specifically motorcoach-friendly (there are campgrounds that accept RVs but not larger motorcoaches, so this is something to keep in mind). Again, there are some good books out there listing motorcoach-friendly campgrounds (one being the "Trailer Life RV Parks, Campgrounds and Services Directory" which is updated yearly) that could be used as the basis for POIs of this type.

Another POI list I'm very surprised hasn't been done--and would be incredibly useful--would be a list of RV dealerships, stores dealing in RV equipment, repair places, and so on (I've never seen anything like this for dealerships, some RV clubs do have stuff like this for their own members in book format (if memory serves me right, Good Sam does publish something like this), and the only lists I've seen of RV goods stores tends to be from big chains).

Most folks I've known who've used "regular GPS's" for this sort of thing have used a combination of tactics--lists of truck stops or features from truckers' POIs, as well as their own additions. (I don't think the perfect "motorcoach RVer POI set" has been made yet--it does give me some ideas, though, just based on my own limited experiences with motorcoach travel. If you've got suggestions as to the sort of thing you'd like to see...)

EDIT: Turns out there is a group that is working on a POI database for low-clearance overpasses here. May well be something worth checking out.