Rotisserie cooking help please

Hi all, this is my first post and I need some direction on using the rear burner if I could please. We did a small prime rib last weekend on the rotisserie just using the rear burner and it turned out great, a little past medium but that's because I have a cheap temp probe and will be fixing that issue this weekend with the purchase of something new. My question is, when using the rear burner, are you supposed to use the main burners as well or just the infra-red one? It took two hrs to do the roast and for the most part it was fantastic. We are doing a 9lb prime rib for x-mas and I'm not sure how to do it now that we have increased the size. As for the temp probe, I can't use a wireless or wired one as I like to use the rotisserie so much so I need to look for an instant read type. Any suggestions / help on how to cook my 9lb roast would be greatly appreciated.

Actually, any tips in general about using the rear infra-red burner would be great as there was nothing in the manual and it has been hard to find much on line.

Thanks,

Jason.

I have a Barbeques Galore Gas grill and the manual specifically states NOT to use the other burners when cooking with the rear rotisserie burner. I would imagine this is the case for all gas grills with rear rotisserie units.
For temperature monitoring during rotisserie cooking, I use my polder probe thermometer and start probing periodically when I feel the cook is nearing completion............increasing the monitoring frequency as the required meat temp approaches. This has always worked for me.