I haven't used TPO in an RV application, although like you: ours will need replacing in the near future. TPO is the way I'm leaning as it's more of a resilant material compared to epdm. From past expierennce in commerical building applications I've seen the durabilty, but the installation is much more tedious than epdm.
EPDM is great but can tear more easliy than tpo. Unlike epdm tpo needs its seams welded with a special welding iron and rod. In your case depending on your rv size you might not need to worry about seam welding, but depending on your rv roof profile, you might have to miter some of the corners and then the seam welding would come into play
keep us up todate with your project and good luck
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