PUMS has a variable GRPIP, which is gross rent as percentage of household income. I’m not finding it in the IPUMS variable list. Do you not use it? I can’t seem to reproduce it from gross rent and household income.
You are correct that IPUMS USA does not offer this as a harmonized variable. However, you can get this as a source variable (sample-specific, unrecorded version of the variable); for example, see US2021A_GRPIP. I will make a note that it would be nice to offer the harmonized version of this as well so you don’t need to download the sample-specific variable separately.