There are films a lot lighter than monokote, but I thing most will be to heavy for the light balsa frame planes. Besides the weight though, the shrinking will likely break the small sticks in those models. You might try the "Club house" or the "Off Topic" forums if you don't get the answers here. If I remember correctly, there was some very light silkspan that could be used for those models. I haven't done anyting with them in 40 years though, so there may be covering that I don't know about, or what I do know about may not be avaiable any longer. Good luck.

Don