There a few choices: Laplander bags ? Waxed Porteur Rack Pack < This is a porteur bag that turns into a backpack.

Another is Freight baggage, they also sell a porteur bag with backpack capabilities, but I would not recommend. Really bad customer service, and never actually shipped the bag I ordered after 3 months of waiting. Took another two months to get a refund which I had to do through my bank.

My favorite set up is basket and Rivendell Sackville. Sackville ShopSack - MEDIUM - half n half . You can take the fence off the porteur I think, and zip tie the basket on. Wald 137 fits Riv medium.
This is my current set up. For bike camping, I just strap my sleeping bag to my saddle. For longer touring, I have low riders and front panniers. The medium sackville has a lot of space inside, and has places on the side to attach a shoulder strap if you need it. The sackville also comes in a much larger size. If you're carry a lot of weight, you might wanna have a compression strapped from the front of your basket to the handlebars for extra support.