Here's a link to one possibility Doug ... I bought mine through Digikey but you could also try Newark Electronics.
These have a heatsink-surround and mounting holes to bolt directly on the firewall inside the cabin.
Jeff
https://www.digikey.ca/en/products/detail/ohmite/HS25%25205R%2520F/5969800?utm_adgroup=General&utm_source=google&utm_medium=cpc&utm_campaign=PMax%20Shopping_Product_Zombie%20SKUs&utm_term=&productid=5969800&utm_content=General&utm_id=go_cmp-17855401585_adg-_ad-__dev-c_ext-_prd-5969800_sig-EAIaIQobChMI6d-fws6SiAMVfRStBh1d3QxeEAQYAiABEgJ7AvD_BwE&gad_source=1&gclid=EAIaIQobChMI6d-fws6SiAMVfRStBh1d3QxeEAQYAiABEgJ7AvD_BwE

-----Original Message-----
From: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Monday, August 26, 2024 6:00 AM
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: flyrotary Digest #5414

 1) Peak and Hold External Res placement
    by "DOUGLAS LOMHEIM dlomheim@aol.com" <flyrotary@lancaironline.net>

This digest is sent to you because you are subscribed to
  the mailing list <flyrotary@lancaironline.net>.
To unsubscribe, E-mail to: <flyrotary-off@lancaironline.net> To switch to the FEED mode, E-mail to <flyrotary-feed@lancaironline.net>
Send administrative queries to  <flyrotary-request@lancaironline.net>