I Had a Cheapo Aluminium Beam racks a while back on a (Road) commuter which I used daily with a 20L Drybag, I eventually replaced it with a posh Vaude seatpost mounted bag, and binned the Beam.
But I've got a planned bike packing trip coming up and I intend to lash a ~15-20L Drybag to the arse end of my bike again (Gravel or MTB yet TBC) I do have a full rear pannier rack that will work (on the gravel bike only) but it's a bit bulkier than I really wanted TBH and I won't be using any side pannier bags, just a big old drybag.
The default answer seems to be a Tailfin rack these days, But I just can't justify £100+ on a fancy rack for occasional use and all I really need is a rear platform to lash a drybag to.
I can grab another one of those Beam racks for about tenner online, I'm thinking I could actually just clamp it to the (Al) Seat tube rather than the Seat post (Carbon/Dropper) and based on my prior experience of them this would be a reasonable solution to stabilise a rear mounted Drybag at a relative fraction of the price of a 'proper' Tailfin rack. Anyone else used one of these in anger for (on/offroad) bikepacking, any compelling reason it wouldn't work?
