Just wanted to add some comments from experience on seatpost slippage...

1) Seatpost clamps are not all the same - some can provide a much tighter clamp than others. The stock Xootr ones (at least they were stock 13 years ago) are not that great - Peter Reich sent me some better ones but not branded so I can't tell you what make they are.

2) Seatpost clamps need lubing too. Not all clamps use a cam shape sliding in a socket (the ones Peter sent me had an internal lever point)- but for those that do, keeping that friction point lubed can give you a lot more leverage.

3) grease did work for me (by making the post a tighter fit) but it makes a mess - particularly annoying when loading into cars. Better than grease is a wax-based dry lube - does the same job but won't make as much of a mess.

4) You can speed up your unfolding as well as solving your seatpost slippage by hacking up something for the seatpost to stop against when it gets to the right position. I use a piece of tubing inserted down the seat tube all the way down so it rests on the BB shell. The top of the tubing has to mate well with the bottom of the seatpost. To aid maintenance I've fitted a spring clip across the diameter to give me something to hook on to on the rare occasion I need to fish it out. So when unfolding the bike I simply slide the seatpost down until it stops, then clamp up, but if the clamps are not 100% tight it's still not going to slip. (I still want them tight though as that's part of the structure of the frame).