Let $F$ be a Maass cusp form for $SL(3,\mathbb{Z})$ (level 1 trivial character).

Let $g$ be a Maass cusp form for $\Gamma_o(N)$ with character $\chi$ mod $N$. For convenience, you may assume $\chi$ is primitive mod $N$.
You may also take $g$ to be an Eisenstein series $E(z,s,\chi)=\sum_{\gamma\in \Gamma_\infty\setminus \Gamma_o(N)}\bar{\chi}(\gamma)I(\gamma z)$.


If $g$ was leverl 1 (full modular group $SL(2,\mathbb{Z})$), 
then we know the Rankin-Selberg $L$-function of $F\times g$ is a nice integral 
$$\text{gamma factors}\cdot L(s,F\times g)=\int_{SL(2,\mathbb{Z})\setminus H} F(\begin{pmatrix}z&\\&1\end{pmatrix})g(z)Det(z)^{s-1}dxdy/y^2.$$

The standard unfolding technique applies nice line to the Fourier-Whittaker expansion of $F$. See page 372 of Goldfeld, Dorian. Automorphic forms and L-functions for the group GL (n, R). Vol. 99. Cambridge University Press, 2006.

However, when $g$ has higher level with character, I don't know how to define the integral. That is my question.

Also, remind that if $f$ and $g$ are automorphic forms on GL(2) with characters $\chi_f$ and $\chi_g$ we can define their Rankin-Selberg $f\times \bar g$ by using some Eisenstein seires $E(z,s, \chi_f\bar{\chi_g})$ to balance the characters of $f\bar g$.

And for my question, adelically, there is definite answer. But I am looking for something computable in classic settings.