Your engine is a great refining/distillation unit. Condensation won't hurt the oil a bit and it will distill off as soon as you reach operating temps. On new (last 15+ years) the manufacturing processes and most of all, Fuel injection and ECU's keep your oil MUCH cleaner than years ago when 2000 miles changes were often recommended. I assume like most RV's your trips are typically not short in town ones. Those are by far the worst on oil and even those aren't nearly as bad as the old carb'ed days. If you want to feel better, after your next oil change send a "sample kit" in and have in analyzed. You will find that after even 6,000+ miles of highway use it will test close to new. (The suggestion above of 5000+ miles or once per year is a good rule of thumb.)
Unless you are doing a lot of VERY cold winter driving, or VERY hot summer driving (while towing) a synthetic is not usually worth the investment. (Clearly synthetics are better than stock dino oils, but overkill for the price with your change frequency and application.) Contrary to popular opinion and Madison ave, it will not give you any additional HP or MPG. (except in the cold extremes with short trips)
I have dynamometer tested probably 30 brands of synthetic and dino oil on dozens of engines for several companies and race teams. With measuring resolution of fuel use per seconds and HP in the 1-2 area, I have NEVER SEEN any advantage with synthetic at normal operating temps and application. There are some "semi-synths" that give you a slightly better oil for a much lower price if you want.
BTW, In all our tests performed for a large chemical company (tested about 20 brands of off the shelf brand name oils in misc weights, concoctions etc.) we only found 1 brand that concerned us in quality control (varying mixes from batch to batch) and even it performed flawlessly, meeting all expectations. (BTW, obviously a good brand name filter should be used at every change.)
To be fair, I use synthetic, but I get it much cheaper than retail