^ And how old is the van?
When you say 302 I presume you mean mid 90s or older. You have a 20-30 year old truck that isn't very robust for towing duty in the first place. (1/2 ton vans typically aren't/weren't equipped for heavy towing)
If it doesn't overheat during normal driving then there is likely not a huge problem.
I'd start with the easy, cheap and likely stuff.
Coolant flush (coolant over 5-10 years old?) $50, new thermostat when you have it apart to flush, $10, new radiator cap, $15, new fan clutch $50 tops.
If that doesn't cure it, you probably are doing too much with an old truck without digging deep into it.