I think you could make the Crossfire work with those wheel covers without a problem.
We are planning a trip out west next year as well. I bought a spare tire and rim and the Roadmaster Spare Tire Carrier as insurance.
Even though I have 19.5" commercial tires, I installed the Crossfire. Without it the tires start out at the same pressure but after an hour or so of driving there can be a few PSI difference in pressure and a few degrees in temperature. The Crossfire gives you the best possible wear and performance for your rear tires.... and it is nice walking around the coach and the indicator telling you if both tires are properly inflated before you get in and turn on the TPMS.
Good luck!
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