You obviously have a helluva lot bigger trailer and tow vehicle than most of us here, Clois...! And, obviously, you 'race' while I just 'do track events'.
I've found that good preparation eliminates most of the need for work in the pits. I take a small compliment of hand tools, and keep a 'special' set of tools in the trailer at all times. My approach is that I need to have enough with me to replace items that may fail...but only those items that I can replace in a couple of hours. I don't have a 'pit crew'...it's me....I do it all....change tires, fuel the car, drive the car, park it, load it, unload it, etc. etc. etc.
I have enough with me to replace a fan belt, radiator hose, sparkplugs, change tires, etc. I carry hand tools, jack stands, floor jack, radiator hoses, couple of fan belts, pre-gapped sparkplugs, couple of fuses, light bulbs, race wheels and tires, some brake pads, and that's about it. If something breaks that requires more than a couple of hours to repair, then I figure the weekend's done for me...time to sit back and drink!
Seriously, if something breaks to prevent me from driving, I don't want to spend all weekend trying to repair it...those repairs are better done at home in the relative comfort of the garage without the 'pressure' of needing to hurry to get back on the track. Chances usually are that in our haste to repair something, shortcuts are taken, sometimes causing more damage and compromising our safety. I'd much rather load up the car in these circumstances and simply set back and become a spectator for the rest of the weekend than spend a frantic 2-3 hours under the car trying to replace a part just to get another 20-25 laps in. It doesn't seem like it's worth it to me.
Just my opinion here, Clois...and we all know what those are worth, don't we...?
I fly R/C airplanes as another hobby, and have done so for almost 20 years. I have a theory about those who have tried to repair an airplane, engine, or radio at the flying field. My theory is that if it doesn't work at home, it sure as hell won't work at the field. Check out all your equipment at home BEFORE you come the the flying field. Then, if something breaks at the field, sure you want to fix it. But...limit your repair time to 15-20 minutes. If you can't fix it in that length of time, you're probably going to force something and expose yourself to all the errors of omission that come with that self-imposed pressure to get the plane back in the air! I've always tried to teach student pilots the same philosophy...15-20 minutes work time. If you can't fix it in that length of time, load it back up and take it home for the repairs. I've had many guys I taught to fly come back and say that was some of the best advice they've ever received, and that once they got the plane home they discovered other items than needed attention and continued flying may have cost them their entire plane.