BTW I aborted my project today. After spending several hours on the roof, prepping the base and looking for the cross-members, I finally gave up. The only cross-member I could find for sure was in the wrong place and wouldn't allow the dish to clear a skylight when in the down position. All the others were elusive. I'm leaving for a mini-rally, so I'll try again when I have more time next week.
Do you have, or know anyone who has a metal detector? You know, the ones you see guys trying to find coins with around the campgrounds and beaches. If it is a good one, you should be able to pin point the roof cross members exactly, if they are aluminum. I know the one I have would do it.
It would be nice to know if Monoco was precise on their spacing of the roof rafters, most likely they are ,(ie) houses are set at exactly 16" on center. Since you have found one rafter,you should be able to measure to the next one.? ??? And with a very small drill bit, find exactly the front and rear of the rafter. Then with a small amount of epoxy fill in the small hole.
Monaco's roof drawing shows the spacing between centers of the gaps, but not spacing between centers of the cross members. Typically, the dimensions specify distance between centers of 3 gaps (not each one), and the dimentions tell me they're not equi-distant. So, it would be a craps shoot to find a specific cross-member.
BTW the one I found happens to be visible at the refridgerator vent and the drawing shows it going right across the coach from there.
I'm liking this idea less and less by the minute.
I realize that some folks haven't even worried about screwing into the cross members, but that fiberglass is quite thin - maybe 3/16". I'm used to drilling and screwing into several inches of fiberglass on the boat. The hull of our old tub is probably 8" thick fiberglass, so you might understand my apprehension about anchoring what is essentially a "sail in the wind" to that flimsy piece of fiberglass on the roof of the coach.
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.
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