Yes, it is wise to impregnate the canvas again after cleaning.
Why impregnate after cleaning?
Every cleaning agent affects the original impregnation. That is why we always recommend waterproofing the fabric again after cleaning to provide extra protection against fungus, dirty water and, for example, bird poop.
Ultramar Sprayhood & Tent Protector is a super-strong impregnating agent. We have developed it specifically for use in our sail and tent laundry. We use it for the impregnation and waterproofing of tents, boat covers, canopies, catering umbrellas and awnings. And with a lot of success.
Do you have a trailer tent or some other tent with cotton tent canvas? Use Ultramar Canvas & Cotton Protector to make your cotton tent watertight.