I have no experience with the SL after 8-10 hours of being parked in the rain, but other canvas (versus vinyl) soft top cars I've had cause me to have a definite preference for getting into a dry car in the morning versus one with a thoroughly soaked softtop. The heaters of most roadsters can't dry out the soft top very fast on the road, and highway speed wind over the top seems to lower cabin temperature significantly through evaporation (a cool idea in the heat of the summer, but not at other times!).

Also, I expect that some of the seals will need replacing, but I didn't want to learn which are highest priority by finding "signal puddles" on the carpet.

I don't intend to start out a trip in rain, but things can change once you're a couple hundred miles from home. Is it likely that a water repellent ("breathable") cover will be sufficient to prevent saturation of the soft top canvas?