Jim is right,unless,by chance You were going to set on a new basement with post n beam down the middle.
I think the roof will be the biggest challenge and most important. you could do a complete roof over. You could also leave the existing roofs and set the homes with a lengthwise slope,then tie the valley together with laminated EPDM layers wich would have a little flex to them or invent some similar system. This,if it worked as planned,should channel the rain from both "inward" slopes from each mobile.Snow load in that valley and/or ice dams could be considerations too. Roof-over sounds better.
Then theres wiring,,would You have seperate services or combine them to run off one service? Either could have advantages,I think the 2 services would be more versatile,but,then You get 2 bills each with all the added charges they tack-on these days. Would make the possible 2-zone heating/cooling thing easier tho. Maybe one larger service panel wich splits off and uses the existing panels as sub-panels.