The ornamental design for a raingaugebase, as shown and described.
FIG. 1 is a top perspective view of the rain gauge base.
FIG. 2 is a front elevation view of the rain gauge base.
FIG. 3 is a right side elevation view of the rain gauge base.
FIG. 4 is a rear elevation view of the rain gauge base.
FIG. 5 is a left side elevation view of the rain gauge base.
FIG. 6 is a top plan view of the rain gauge base.
FIG. 7 is a bottom plan view of the rain gauge base; and,
FIG. 8 is a perspective view of the rain gauge in a folded configuration.
The broken line showing of structural features is included for the purpose of illustrating non-claimed subject matter and forms no part of the claimed design.