Yep, you need to associate tb.exe with the .rlp files.
Though that might be hard, because it doesnt work so well in this 3.8.
Install an older client, like 3.7, that'll make the .rpl as a 3.7 file, then reinstall the 3.8, that'll reset the client version and you'll be able to see it in 3.8.
Unfortunately simply associating doesnt work sometimes.