If you are going to pull a 48 ft trailer, it is going to be over 10k. The trailer itself will weigh between 6-8k probably more and that doesn't leave much for payload. I know it will be more than 3-4k. You don't need to go the IFTA route, but you will need to buy a permit when you enter a state at the first weigh station that you come to that is open. Try to plan your route through states that are "port of entry" states. You can buy permits at the weigh stations. States that aren't, you have to get your permits BEFORE you enter the state. Doesn't cost any more just a pain in the butt. Ok. is one, I know for a fact, a $200+ fine tell me that. As several have told you here, find yourself a DOT officer and tell him what you plan to do, and he will tell you what you NEED TO DO to stay legal. I haul for a living and try to do it right. It's really not hard, but there are rules you have to go by, if you don't, sooner or later it will catch up with you.