A lot of State scales are commonly available, KC, especially those not on freeways but rather on State highways. With the old Pace Arrow, I used to regularly stop at any I happened to pass while on trips, but since getting the Beaver, I stopped doing that; our particular model has so much more carrying capacity than most, I doubt I could ever overload it. The only reason I'd stop at a scales might be because I was curious about the weight of a particular corner or side due to some change in my normal loading pattern. When we had the RVSEF weigh us in 2007, loaded to the ceilings, I recall we still had 3400lbs. to go, if we could find that much storage volume somewhere - short coach on heavy chassis is likely why.
I might suggest the State scales just below me on Highway 212/224 between Clackamas and Carver junction, just east of 142nd Ave., on the north side of the road. I rarely see any trucks using it, and only about half the time is there an ODOT officer manning it. Just drive in from the east entry from the left turn lane (if coming from Thiessen across I-205). I've yet to pass an empty Oregon scales facility where the scales weren't left on for anyone to use; the digital screen is on a pole in front of you and easily seen. If there's a truck already there, just be patient and wait your turn. Then there's no hurry unless a truck comes in behind you, but I've never had that happen at the 212 location... it's always been empty. If it happens to be manned when you arrive, they likely will be happy to assist you.
If you have occasion to go over Mt. Hood, there is a scale near Brightwood as I recall. You could also check the State ODOT website - they probably list scale locations.
5 years timeout on the tires is a bit extreme. The standard seems to vary depending on who you talk to. A local mechanic the other day suggested that as long as there is no cracking, alligatoring, or other noticed flaws, he'd not buy new, especially with minimal miles (16,000 on mine) and very little solar exposure. He does a lot of business with the Clackamas Les Schwab's, and they are a good outlet that I've also purchased from for several decades. I've had more than one Les Schwab dealership, including Clackamas, run a routine inspection and tell me the same thing as the local mechanic. But most here follow a 6-7 year guideline I think, and my Goodyears are at 9. Most of that was parked here by the house, esp. the last few years; lack of travel and intra-tire chemical stimulation is a good reason in itself to get new ones.
As Dave discovered, the Toyos are significantly cheaper even than the Michelin Advantage deal. If you buy at Henderson's, that doesn't mean you can't get service from any other dealer of that brand anywhere in the country. Les Schwab has done free leak/plug repairs several times on tires I didn't buy from them, and I send my daughters and grandkids there for tire repairs. They've also fixed non-automotive tires for me at no charge. That's one reason they built such a good reputation and successful business when Les was running the show. If you are still concerned, I'd seriously lean toward the less costly Toyos from either your Milwaukie store or Bob Dickman's Les Schwab in Junction City.
I'm still up in the air on which brand and dealer, but will have to decide before too long. Henderson's would have to order Michelins out of a Roseburg warehouse, and I'll want them to check the date codes at the warehouse first. Bob Dickman is a busy motor home tire facility, that likely has their own stock, and moves enough tires that perhaps they normally have newer codes; I haven't talked to them yet. Still trying to juggle our personal schedule. Henderson's has state-of-the-art balancing equipment, which after having Goodyear Portland use theirs to discover anomalies in our Monaco factory wheel weight installation that caused a slight vibration, is important to me. I'd think Bob Dickman's would have modern digital balancers also, due to their sales volume for large tires, but I don't know for sure as yet.
-Joel