Thank you to all who responded.
CWSocial: I'm going to buy the UK Vodaphone SIMs on Amazon for $4,97 each (need 2) based on your excellent posts on how to set up, activate and top off.
I will be in Europe for 30+ days, (39 days) so I will purchase the Big Value Bundle, and I will purchase a second bundle while I'm there. I have a PayPal account, so hopefully that will work while I'm there.
Since I don't leave until mid-April, I will purchase the SIMS on April 1, to have time for delivery and to set up, unless somebody has a reason I should buy them now. I like setting up and testing while I'm here in the US to make sure everything works, but pop the SIMS out and don't install them again until I land at my destination airport, I install the SIMs while I'm waiting for my bags at the airport. (I carry the SIMS in a contact lenses container and tape a paper clip to it)
The only new variable this time around is that I have a dual-SIM iPhone, so I will need to have my US number put onto the e-SIM slot so I can use the Vodaphone SIM card.
I will report back after my trip on how it went. Thanks for the info.