I have looked into this more, and am seeing an awful lot of guys recommending a 5-point harness over a 4, due to submarining from a front end collision. Also they noticed the harnesses riding up to high as the day do goes on because the 5th point isn't there to hold them down. Any thoughts on this? I noticed Pro-Armor also has the 5-point model of your harness, for slightly more, but I wonder about attaching it with out seats, since the bottom pops out for easy access...
I'm one of those that are in favor of the full 5 point harness. I prefer the shoulder straps to be a bit loose, such that it is possible to twist a bit in the seat in order to look toward the rear or lean out of the cab a little bit to see alongside. It is also just plain more comfortable. The crotch strap simply keeps the lap belt from riding up and holding you back, through the soft under-belly. The lap belt should be pulling down and not back. With the crotch strap secured, it will be snug across your pelvic bone structure.
These pictures are from my install in an '04 Rhino. The general principle should be applicable to anything remotely similar. When I first did this, I simply used an extra long Tee plate, similar to the plate that anchors your lap belt to the bolts in the frame. I bolted it down under the seat anchor post and it stuck out far enough for the strap not to interfere with the seat hold-down latch. The pictures show a fabricated anchor plate that has a thin sheet metal clasp that provides additional vertical stiffness by grasping the bottom of the front under-seat cross plate. The sheet metal clasp is spot-welded onto the bottom of the thicker anchor plate itself. The lacing of the crotch strap webbing has to be done such that the webbing does not interfere with the handle of the seat hold-down latch. Not really a big deal, as the harness will hold both you and the seat down in place in the case of a rollover.
Food for thought. This anchoring has been done in many different ways. Ranging from bolting to the floor to additional crossbar tubing being welded into the machine.
5 pt crotch strap anchor:
5 pt crotch strap lacing:
Tee plate alternative: