Good 3M tape will work.
Front-to-back level, front right side of frame; attached with 3M industrial tape since October 2012....(only problem is the white lines have faded, but can still determine level)
Side-to-side level, front right of frame; attached with 3M industrial tape since October 2012 (also lines are faded)
Side-to-side level, attached to the top of the roof assembly. Two holes, plenty of sealant added to each screw hold and screw, as well as dicor around the outer edge to keep it waterproof.
(Need to paint the front frame with some POR; appears to be a little rust.)