Faced the same decision earlier this month and opted for a new truck with a great end of year deal. If you hope to continue RVing for 12 more years, then the '05 is probably going to need to be replaced at some point during those 12 years. So, the question to be answered, is this the time?
My truck only has 87k miles on it, but is now 11 years old. If a new truck last me for another 11 years, I will be 76 at that time and probably RVing less. But in the next few years I still want to make some long trips, like to Alaska, hence a new truck makes sense now rather than later. The '03 is beginning to have injector issues and I am still undecided about selling it as is or replacing the injectors before selling it. My situation is also complicated by moving the custom utility bed to the new truck and needing to put a used bed on the '03 (next month) before I can sell it.
Since your truck is slightly newer you could wait a few more years, just be prepared if major repairs become necessary. And if you replace it with a newer, but used truck too soon, then you may also be faced with a second tow vehicle transition during the 12 years. Good luck with your decision.