2005 T139 ? Pictures?stereo model ?. Sorry but you are not giving much info to go on to aid your replacement. You might have to source it through a RV Dealer. Possible for it to be several models that will fit the opening. When I received my new 2015 FF 210uds it had a cheaper stereo and I made them change it out after I took possession. Tech said there is many models to choose from. Silverado
We bought one of these to replace the very dated (can you remember cassettes) stereo in our project trailer. The price was right. We made a custom cabinet for it that goes over the tv and holds dvds and cds as well. But it is large for your application probably.