dan-nickie
Grand Prairie, TX
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Was mounting a Sat dome to the roof today.
The mounting brackets had # 12 sheet metal screws.
When I drilled the pilot holes, I could tell the roof material was very thin. Seemed it was less than 1/8 inch thick.
Then when I screwed down the #12 screws they would not tighten up. The would just keep turning as if stripped.
The pilot hole was only 1/16 drill bit.
And I did not use a power driver, just hand held screwdriver.
I have read on other threads that there is wood under the rubber roof, but this seemed to be maybe thin fiberglass or something.
Is it possible that it is not wood under the rubber?
Any suggestions on how to make the screws hold?
Thanks.
Dan and Nickie, Four Winds 31p, Retired Jan/2011
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Twomed
FL winters and then somewhere cool
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Probably what the industry calls "luan"...basically cheap 3/16 plywood. If you can't find some rafters/studs would use toggle bolts. Those and 3M 5200 quick dry, or Eternabond will hold it down just fine. Toggles will require a bigger hole, but will hold for you, just caulk real carefully. 
Happy Trails
06 Monaco Dynasty
07 Hummer H3
FMCA 279843
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Lady Fitzgerald
Tempe, AZ, USA, Earth
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I would use molly bolts before using toggle bolts. Besides not needing as large of a hole, molly bolts don't have a loose toggle that will be lost if you ever remove the screw.
3M 5200 is great when used as a bedding agent and will hold forever. The problems with it is once you use it, it will be harder to remove than even Eternabond (you would probably destroy the rubber). It also isn't UV protected so it makes a lousy caulk since UV will eventually deteriorate it. 3M 4400 would be more appropriate. Eternabond will also work well.
Jeannie
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ScottG
Bothell Wa.
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Normally, the rubber membrane is glued to an outer layer of luan (because it's so smooth) and the luan is attached to 3/8" or 1/2 plywood or in some cases, OSB. But of course your builder could have used aluminum or even fiber glass though I can't think of why they would wan't to cover a nice fiberglass roof with rubber!
Scott, Grace and Wesly
2003 Dodge 3500 4x4, 6 speed Cummins (lightly bombed),
2004 Forest River 25RKS many, many mods.
H0NDA eu2000i
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mwebber78
New England
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I would contact the manufacturer and find out whats under there. My quess, you have a laminated roof so you have a 1/8 piece of press-board or luan. Niether will hold a screw or bolt for long, so the other folks have good recommendations.
Michael 
2 DD's and my DW 
2011 Forester 3171DS Class C
Nissan Altima "The Fun-Box"
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Dusty R
Charlotte Michigan 48813
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Make the hole bigger, if there is foam insulation take an allen or bend a nail and put in in a drill motor insert in hole and chew out some of the foam to make a cavity. Then pour the cavity full with epoxy. After it's cured drill pilot hole and insert screw.
Dusty
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dan-nickie
Grand Prairie, TX
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Thanks for all the replies guys.
I'm afraid to walk on the roof now.
Seems if I step in the wrong place I could crack it.
Anway, now I know what I need to do to secure the dome.
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GrumpyandGrandma
CIncinnati, OH
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dan-nickie wrote:Thanks for all the replies guys.
I'm afraid to walk on the roof now.
Seems if I step in the wrong place I could crack it.
Anway, now I know what I need to do to secure the dome.
The manufacturer may have already had reinforcing in place for a dome, before I went any further I would contact them to see if and where it is. Jayco puts aluminum plates in the roof for mounting Sat Domes.
Grandma in front of her retirement home..
She lets Grumpy drive!!
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oldtrucker63
Harlan Kentucky
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Yes I would say it is 1/8 inch "luan". Nothen to screew to if you miss the 2x2 cross wood. This is why I used 1/4 inch plywood on my roof and 2x4 cross wood.
Without Trucks,....America Stop's
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oldtrucker63
Harlan Kentucky
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Dusty R wrote:Make the hole bigger, if there is foam insulation take an allen or bend a nail and put in in a drill motor insert in hole and chew out some of the foam to make a cavity. Then pour the cavity full with epoxy. After it's cured drill pilot hole and insert screw.
Dusty Great ideal here.
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