We purchased a 2020 Dynamax Dynaquest XL last year. In addition to upgrading the standard mattress with a Serta 3” topper from Menards, which made a huge difference, we chose to purchase RV sheets from Quahog Bay Bedding -
Yes, they are pricey, but they are designed for RVs and are made of wonderful fabrics. They have a drawstring which snugs them to the mattress and are noted with “head” and “foot”. We purchased sheets as well as their mattress pad for our RV king. We especially like the bamboo sheets.