Tap screws and metal prep

[Muskie]

Hi folks
Muskie here... a couple questions regarding C-channel/ floor screwing and frame. I am replacing 2 rotted areas on my 59' Tradewind floor [front and back] and also getting new metal welded to the frame on the back in order to do this.
Understanding that normal procedures are to use elevator bolts through the C-channel, thus through the wood into the frame, could I get away with using tap screws for this? If I was re-doing the entire floor I wouldn't consider tap screws, but for 2 patched areas I am hoping I could get away with good tap screws.

Secondly, to prep the frame for a welder, how much area do i need to prep for the the new metal, and any hints on doing this. I have a grinder to get the rust off, but perhaps someone may know of other methods, type of grinder wheel etc...

The pic supplied indicates only the exposure of the problem. Wood will be cut away very soon for proper prepping.

[markdoane]

It depends on how much of the crossmember you need to replace, and the condition of the frame where you will weld the new crossmember. On my '59 Tradewind, the frame was rusted and I had new 12 ga metal welded over the original frame members, then new hold-down plate in front and crossmembers front and back.
However, even with new metal I would not use tap screws for the front and back attachments. OK to use tap screws for repairs in between, but the front and rear attachments require substantial (3/8" grade 5 or grade 8) bolts and washers to the hold down plate. Tap screws would pull out pretty quickly one you got on the road.

[Muskie]

Cheers, if I understand correctly, the crossmember is the back part of the frame that the bumper attaches to?...thus runs parallel to the bumper. So yes, the whole thing is rotted and needs replacing. Your idea of scabbing on a piece[s] of metal to the what I am guessing are the frame members is a good one.
Basically I need 3 pieces replaced or strengthened. The two pieces that hold the bumper plate on and the what is I guess the crossmember, or bumper plate? If you were looking at the back [birds eye] it would resemble this: !_! All three pieces are in question.

Your point about tap screws is also good. I will go with bolts, you are right, tap screws would loosen, then weakening the whole fix.
Thanks for that.