The price will depend on if your trailer has a LQ or not. THe hardest part of recaulking is the removal of the old sealant. The more accessories and vents that stick through the roof, the longer the job will take to accomplish. A worse case labour time should be about 2 -3 hrs for a non LQ, and almost double that for a fully equipped LQ. Multiply those hours times the prevailing wages and you should have a rough guesstimate. The skills of the person effecting the repair are most important. Properly cleaning the old grout, without damaging the surface, and installing new sealant is not a glamorous job. It is often hurried or given to the least skilled employee. The quality of the replacement caulking is very important to the longevity of the maintenance. A product that costs 50% more than a cheaper version, can increase the weather resistance for almost double the life span. You will spend another $20 -$30 for the caulking, and eliminate several hundred dollars in having the labour charges again applied in only a few years. Recaulking can easily be a DIY affair, and often your pride in ownership, and taking the necessary time, will produce a much better sealed roof than the "professionals". You don't need any specialised tools, and the better caulking can be sourced from many suppliers. | 
caulking trailer
