weird.
With regards to the weight of compost in trunk. I work part time for a friend who owns a nursery delivering mulch, compost and gravel by the truck load. I’m by no means an expert but can only say that it can be heavy if stored outside, though not as heavy as gravel. But if one compact tractor bucket full of compost were dropped in a Mustang trunk, it would definitely be a big issue weight wise…and not for the betterment of the Mustang. Though I can’t vouch for your numbers, your concern is well taken.