another axle location question

hi all. new guy here. im in the process of building a large tear drop. cabin car??? i guess you would call it??. anyway, its fairly large, 7' x 14'. all aluminum chassis and walls to keep weight down without sacrificing strength. i want to keep the tires just inside of the outside wall, so cutouts in the chassis and walls have to be made. i really dont want to use a straight axle, i have an idea about an independent suspension using a control arm, coilovers and a hairpin. ive built hotrods using it , so it should work on a trailer. anyway, i really have no solid idea what the various galley components, mattress, and just junk in general will weigh. is there any rule of thumb as to where an axle should be according to length?? if i do end up using this idea, moving the axle will be a major hassle, and redesign which i dont want to do if i can avoid it. if i can get close, i think i can balance things close enough by moving contents. anyway, sorry for the long post, but any help would be greatly appreciated. thanks, and best regards, j.d.