Tom:
Also being a serious boater (well ex boater now) I had the exact same fears. Like you I was used to attaching to fiberglass so thick you would never punch through the other side. If you describe what you are doing to Monaco, and they give an answer similar to what Newmar gave me, it should not be a problem. Remember you are not asking 3 or 4 screws to do the work, but as I recall, something like 18 or 20 of them, across a nice sturdy wide plate. And if you use that 3M 5200, it is even stronger than screws. I am sure there is substructure under that fiberglass besides the aluminum studs, so find out from Monaco what else you will be screwing into.
Forget about the boat and find out what is there to work with on the MH. I have yet to hear of anyone who tore up their roof installing a Direcway dish.
Jeff:
Welcome aboard. If you have any trouble with the OPI meter do what I did. Throw it away, and train your Admiral to talk with you on a handheld using the laptop while you are on the roof. Sharon has mastered that now and we get ours tuned in in under a minute now. One less thing to carry up on the roof now. ;D
Tell Sue, Sharon says, "Hi!"