B+ motorhomes

Depending on how large the spider cracks are, A good coat of wax to prevent water intrusion may be enough. Use a good past wax and rub out thoroughly. If you think more is needed, boat shops sell Uncle (somebody's) Crack stopper. Clear liquid, runs into the crack and hardens. There is glass behind the gelcoat, so structure is not a problem, but you do want to stop water from getting behind the gel coat and Freezing, which could cause some ugly chips to fall out next year.