ideally short around 120cm. but anything considered.

120 might be a bit small... if you plan on using it on the water... id be looking for a 135ish board.. thats the standard sized board.. i have used a mates 122 and in anything but nice flat water it gets a bit sketchy.

Im sure others will give an opinion as well but 120 i think you will find is a bit small..

i'm planning big down winders with Butch on the landboard. All i need to be able to do is skim accross the esturies on it and then strap it to my back and carry on. big will be too much of a pain when i strap it to my back.

in saying that i will consider a lager board and cut it down to suit. infact an old school fat surfboard style twin tip with abit of boyancy might be the go.

What ever it is it has to be cheap as i'll be attacking it with the dropsaw,jigsaw to mount my mountain board on the top.

ahhh now i understand.. Again tho 120 is really tiny and requires alot more power to get you up and planing than something with a bit more size.. I guess you will have to find a happy medium..

Maybe there is someway you can get a full size board cut it in half across the width and put a hinge mechanism that locks into place only when you need the whole board open... the unlock and fold in half...

yep i've considered 2 and 3 peice boards. lots of idea's are belting though my head. The wholy grail would be a folding board that quickly straps to the underneath of the mountainboard leaving me a few mm of wheels so i can role into the water start skim across and role how without getting wet.

Just get an old bit of marine ply, cut it into shape and bung some straps on. quick and easy and actually rides really nice. loads of info on ply boards on the net. Cheap and easy!
eg....
www.flickr.com/photos/lenny_meriel/62897357/in/set-1166087/

yep i've considered that. infact i have some bendy ply, glass, carbon, foam lurking in my garage right now. So i could start the build right now.... execpt im feeling abit lazy. if i can find a cheepy then thats alot easier than a whole build. currently eyeing some shitters on trademe at the mo.