Thanks for the advice on what to see and the rental agencies, it is much appreciated!
On our last trip we stayed at Grants Pass to do Crater Lake, followed by a couple of nights at Belknap & John Day. We were able to visit the Oregon Interprative Center in Baker City. We also drove along the I84 to Vancouver wher we overnighted.
We picked Troutdale as it had a good write up in the guide books & looked a fairly central location for exploring the Columbia River Gorge. Unfortunately i think we're tied in to staying at the BW as we booked a special rate.

I will check out the holiday Autos website as suggested.