88 350 header gaskets keep getting blown

I just got a 88 silverado with a 350 off a buddy and he says every time he hooks up a trailer it blows the header gaskets after about 10 miles. What can I do to stop this since I want to pull my boat with it. I have seen locking header bolts but don't know if they work. The last ditch effort is to get a set of stock manifolds I guess. What should I do

First off i would say have a good look at the flanges on the headers, they could be warped causing ther blown gaskets. If they are good and straight then buy a good quality set of header gaskets not the cheap ones and after you install them let the truck run for about 5 mins or so to heat them up then re-torque the header bolts. Let it cool down a while and repeat those steps one more time. Then i would say after about a day or so re check them again.