I've been told that I should box the frame on my '67 Volvo P1800S. I know what that usually means (welding in a top piece to make the C-channel frame a box frame), but I've been told something else. The person that recommended doing this said to do that, as well as welding on new pieces on both sides and the bottom. My question is if that is actually necessary if the existing frame isn't rusted out. Thanks for the help.