I don't know what part of the country you are in but some have said Les Schwab tire company is good. We don't have them around here. I wouldn't go to a store where you can tell they do mostly cars. I use a Goodyear Tire place near me that works on all kinds of vehicles, cars, farm equipment, delivery trucks and hot shot trucks. I can stand and watch what they are doing. I don't know any RV place around here that sells tires or works on them. I kind of doubt any would even put the valve extenders on. One of the RV dealers in Lafayette use to carry the extenders but Camping World took them over and their store carries about what you can buy at Walmart.
Maybe ask at a campground near you if they would recommend a tire place or ask a mobil rv service. I would keep trying until you get to where you can check your tires yourself. I carry a portable air compressor and have used it many times. Not many places have air compressors any more. Some you can't get an RV close to and a lot don't even work.
I would read a lot of reviews on the TPMS. I think I have the Pressure Pro but it use to be Hopkins. It has served me well for about 7 years but I find it hard to program. Maybe a newer one would be easier. What ever you get you have to be able to operate it. A tire place is not going to do it for you. I usually take the sensors off myself and label them because they have to go back on the right tire.
I took a picture of my wheel and will try to post it. I post pictures so seldom it usually takes me a lot of bad words and time.
Martha