[jeremyseattle]

I don't know about your year/model, but my 93 Ultra is very sparsely framed. There are inconsistently-spaced 1" aluminum(?) square tubular framing members throughout -- good luck finding them. Interspersed between the framing members is ~2" thick wood-laminated foamboard. If in good condition (not rotted/delaminated from water damage), it actually provides enough bite and rigidity for small fixtures. I use course-threaded wood screws and don't overtighten. No need for pilot holes either.