I changed the single start battery (8D) to a Group 31 which I put in a box like the attached illustration. The GC2 house batteries are located in 2 groups between the engine stringers in similar boxes (2 x GC2 in each box). These boxes are very heavy wall plastic, made by a local company - www.centuryplastics.ca.
I am actually going to eliminate the separate start battery and rely on the house battery for cranking, with the backup being the generator to put charge back in the house battery. Gen hass its own G31.
The Group31 appears to have been inadequate for cranking the port engine (stbd was already cranked by the house battery), so during 2023 season I was, de facto, using the house set for starting.
I think this proposed arrangement will add simplicity and also help de-clutter the engine room (I am a strong believer in having easy access around the engines.