I just ordered 4"x50' rolls of roofseal eternabond tape. I found it at Big Rock Supply
The price was awesome, I didn't get it yet but, it seems like alot of other happy customers.
I am not sure about rules on posting actual prices. However, it was less than Amazon and some other roofing supply places even. I called two local RV dealers and spoke to the parts managers to see if they would match the price, I'd even pay the shipped price to get it local and they flat out told me that the price that bigrocksupply.com has them for is below their actual cost.
It's all volume I'm sure.
If the moderators are ok with it, I can edit with the price I paid but, otherwise if you are in the market for Eternabond or just thinking you might need to get some to have (5yr shelf life) then it's a really good price.