RTP Full Funding Act of 2020 This bill addresses provisions regarding the recreational trails program. Specifically, the bill requires the Department of Transportation (DOT) to carry out an assessment of the best available estimate of the total amount of nonhighway recreational fuel taxes received by the Department of the Treasury and transferred to the Highway Trust Fund for the period covered by the assessment; the Federal Highway Administration to establish financial management information system codes for certain motorized and non-motorized use projects, including single and diverse use projects; DOT to reserve certain amounts of the state apportionment of funds each fiscal year for administrative, research, technical assistance, and training expenses to carry out the recreational trails program; and states to obligate a specific amount of reserved funds each fiscal year for the recreational trails program.