Pre Trip Maintenance

The rear main engine seal should not typically be leaking on a 2004 truck with 95K miles on it. As long as there is no oil showing on the driveway, I would not change it out at this point. However, for peace of mind, I would get a rear seal and an oil pan gasket to carry with me so that if I did need to get it done, I would have the parts necessary for any competent mechanic to do the work. You might want to look up what the exact procedure is to change the seal so that you know what parts are required. Some can be changed by dropping the pan, but many others need the transmission removed. Might be additional parts required to complete the entire job.

Just as an aside, I had a weep on my transmission output shaft seal and it lasted for 3 years until this spring when it suddenly let go with a vengeance!!

I am in the process of doing the same on my truck, for our trip to Oregon.
I wouldn't worry to much, if it is just weeping a little. If you can get a socket wrench up to the pan bolts, check and make sure they are not loose. Don't crank on them though, may cause the seal to split or worse. I always carry extra fluids for the truck, you never know when you need to add some.
Good luck and safe travels

That rear main seal area is a tricky one. Fluids tend to accumulate there as it is a low point and inertia drives leaking fluids to the location. I'd clean it up real well and watch it.

I assume you wouldn't get the oil seal changed yet if you weren't going on a big trip? Given you aren't heading for a 3rd world country where finding spares or mechanics might be a problem, I would just take some spare oil with me and keep an eye on it. Worst case you'll have to find a garage on the trip. I guess if you wanted to be more careful you could always source a replacement part so if you need if fixed and find a garage you aren't stuck because they'll have to order one and that will take 3 days, etc. But then I come from owning Land Rovers - they always leak and it has to be a really big puddle of oil on the driveway to bother doing anything about it.

But I did find a leak that appears to becoming from the rear mail seal. Haven't seen anything on driveway so it either just started or is very minimal. What do you guys do in this situation

The situation(as described)is you don't now for sure, so why pay $900.00 to change what you aren't sure of?