Freighters which contain fighter bays should not require to have cargo space. In theory this should be easy fix. "No cargo space!" is error message in ship design, which would be good point to start checking if this is easy fix.

const std::string fix_key = "_IKEY";
auto n_parse = SerializeUtil::load_string(fix_key + "=" + value);

1. change fix_key to std::string_view, or "static constexpr auto[]"
2. Concatinating strings like this is expensive. Take a look here: https://github.com/splinter-build/splinter/blob/15-default-values/src/string_concat.h