Ok Ok!!!
With apologies to Helmuth von Moltke the Elder, I discovered that measuring/planning fall flat when confronted with reality. I measured a bunch, and created this mock up
I bought 4' lengths of 1"x1" 1/8" steel tubing and used the mockup to create the angle cuts I needed. But the dimensions of the mock up materials are not 1"x1", so the angles where slightly off. Nothing the grinder couldn't fix, but less than perfect.
Design principles included:
- available metal was only 4' long
- avoid damaging the roof of the truck in the event of huge cabin/truck bed flex
- KISS
- make it strong, but don't go crazy
The latter meant I wanted as much of the 4' length under the cabover as possible to give the attachment points as much strength as possible.
KISS meant I used someone else's design and the same dimension hardware throughout.
http://www.wanderthewest.com/forum/topic/9879-wind-deflectors/page-5#entry112124
All bolts/nuts are 1/4" I used T-Nuts in the cabover bedding area, and cut threaded rod to length. The bolts used to attach the wooden fairing to the frame are 2" long, with washers on both sides, and slopped on SIlkaflex to keep them from loosening. The Silkaflex is what I used to "seal/glue" the surfaces where metal meets wood - 1) the fairing itself, and 2) the metal frame to the underside of the cabover. I decided NOT to use 3M 4200 or 5200 because that wood simply isn't strong enough to warrant a glue that tough. The painted surface would pull loose way before the 3M stuff let go.
As for flex and roof damage, once I had the fairing frame welded up and test installed on the camper, I put the truck up on two Rhino ramps, on opposite corners to induce max flex. The difference in clearance was almost nil, which inspired me to keep going knowing it would be unlikely on the roads that I drive that I would ever see 2" of flex and thus damage my roof.
Here are some more pics:
Installed on camper/truck
Pax side 1
Pax side 2
Driver's side 1
Driver's side 2
Clearance at camper roof
Clearance at truck roof