Awesome story. You are making a wise choice and I hope you have a great trip and reunion.
It's super easy to remove the bench seat(s). So, unless you have a bunch of people going, just take it out and leave it at home as it would be a whole lot more comfortable sleeping on the floor. A big foam pad (or one of those blow up beds) for underneath and a bunch of blankets (or sleeping bags) above and you'll be fine....unless it just happens to be during a rare cold snap.
Don't forget that, if you go over any of the passes (almost impossible not to), you will need to have tire chains for the front tires along just in case. If you get them at Les Schwab, they are more expensive, but you can return them if not used (just don't lose the receipt!). Or just get them at Walmart as they are probably a lot less expensive than Schwab.
Hwy 20 east to I84 would be the quickest and shortest route. About 3 hours to Bend and then another 12 hours from Bend to SLC (have driven it sooo many times). Tons of good places to stay along that route too.
Safe travels and Happy Birthday.
