Thanks for the ideas. I am going to call Apria and ask about the portable concentrator. That would really help us over the tanks we carry and the traditional style concentrator. If all else fails, we will try the closet or bathroom with a 50 ft line.
The local Apria office here provides rentals for POCS and the rental fee was $250.00 a week and came with 3 back-up batteries and a o2 supply kit and a humidifier bottle and adapter kit. I have the Sequal Eclipse 3 and it weighs about 15 pounds, it is really heavy, but has wheels and can be wheeled around like a small carry-on or attached to the back of a wheel chair in its assessable carry bag. It goes up to 6 lpm on pulse dose and 3lpm on continuous dose

It won't let you go over 3lpm on continuous flow. It was well worth the $$$. I purchased one outright since renting was about $500.00 for the 2 weeks were we there. I paid $2800 and that included the wheeled case, humidifier adapter, and the micro cannula's and an oxygen tubing kit that had like 20 peices of more tubing, cannula's (4ft and 7 ft) and the cover case to protect it from weather.
I do not take my POC to the parks, I am too afraid of having someone take it. It is an expensive piece to just replace w/o batting an eye. Also, I wouldn't know how to secure it on the rides that we get on. I usually take my m6's with me and have 3 spare bottles that I keep in first aid till it's time for me to change out then I keep them in a rolling back pack to keep them together in first aid. The ladies are great in there and they even let me use a quite room to take a break when needed. I think you should check them out as well
Since I think you said that the o2 use was for night time use only, then please disregard the part about the park. A POC is less noise than a full size, since he is using it with his bi-pap, I will assume that he can't be using more than 3 lpm. If the expense of renting the portable one is too much, just use the free one. Apria charges for the POC yet they don't for the big concentrator and tanks! Good luck
PS, there is a great link made by Sue IN MN for the disability thread you can find it here
http://www.disboards.com/showthread.php?t=595713:thumbsup2