If budget isn't too much of an issue I'd go with a Soma or Surley frame and build to suit, not certain there's a lot of 7sp only, bikepacking capable bikes on the market. I'd guess you can get in at under 1000.00 since there isn't an amazing drive train to add, just build the nicest wheels possible, an origin8 crank with chainguard on one side to protect pant legs and basic components all around. Should be an easy build. Thinking on simplicity, this
https://www.bianchiusa.com/store/git...eed-cream.html
would let you get started really affordably and make the wheels the priciest thing going. You've got me thinking this might be something I do.
One issue I do see is the the trailers often attack to the axle, you may have an issue with that but some you can change the attachment to clamp the frame, if you do that first wrap the stay with a thin layer of handlebar tape, that'll keep the frame safe from the clamp.