Not sure about aerolite but most RV's are just 2x2's supporting luan sheeting covered by glued down rubber sheeting, with some insulation between the exterior luan and interior ceiling luan. If the 2x2's are still good then just screw on new luan and add insulation then paint the roof with EPDM rubber.
If you must replace the 2x2 then you may need a good miter saw to cut angles and bracing to ensure the walls stay 90 degrees to the rafter pieces while you replace the 2x2.
If you are just looking to keep the rain off and do not care about appearance or insulation, paint the roof with tar flashing patch, throw a tarp over the roof and hold it down with lath and screws.
