Amp caddy has different options. It has a claw that you can attach it just about anywhere - I’ll take mine off and attach it to our tailgate tent at the beach. Waterproof too.

Edit: I have the $79 one and it’s loud!

Golf Speaker with Mount, 40 Watt Bluetooth Portable Ampcaddy Version 3 Pro Max Bluetooth Speaker and Mount with Loud Stereo Sound and Bass Boost, 12-Hour Playtime, Extended Bluetooth Range, Waterproof https://www.amazon.com/dp/B081YNKNTP/ref=cm_sw_r_cp_api_glt_i_P9WWNWK647Q9ZY1MZFFF?_encoding=UTF8&psc=1